1. Field of the Invention
The present invention relates to cylindrical domain memories having a storage medium constructed in layer form and consisting, for example, of magnetic garnet or orthoferrite, in which the cylindrical domains are magnetized at right angles to the layer plane and in a direction opposite to the magnetization of the vicinity of the domains and to that of a magnetic bias field. More specifically, the structure is provided with a, preferably, periodic propagation and manipulation pattern the individual elements of which consist of magnetizable material, in particular a magnetostriction-free Ni-Fe alloy, and are applied in the form of layers to the one layer of the storage medium, and a rotary magnetic field is directed parallel to the layer plane for causing the cylindrical domains to be displaced along a path defined by the manipulation pattern.
2. Description of the Prior Art
In the rotating magnetic field, the individual elements of the manipulation pattern produce stray magnetic fields which cause the cylindrical domains to travel to energetically favorable positions on the individual elements. When the rotating magnetic field is rotated in the layer plane these energy minima disappear. They are replaced, at other locations of the manipulation pattern, by new minima toward which the cylindrical domains travel. With suitable manipulation patterns, on one full rotation of the rotary magnetic field the cylindrical domains advance by one period of the manipulation pattern, i.e. by one storage position. In a constantly rotating magnetic field, the cylindrical domains can be propagated along paths which are predetermined by the manipulation pattern.
By providing long, closed loops (so-called "storage loops") it is possible to construct serial memories. The binary digits "1" and "0" are represented by the presence or absence of a cylindrical domain at a point of the manipulation pattern. The information input into the storage loop is written in and read out by way of a write-read loop. The information is not tied to a fixed storage position, but circulates in closed paths of the manipulation pattern. Manipulation patterns of the above-mentioned type are described, for example, by Mitchell S. Cohen and Hsu Chang in their article "The Frontiers of Magnetic Bubble Technology", published in the "Proc. of the IEEE", Vol. 63, No. 8, August 1975, pp. 1196-1206, and by Franz Parzefall, Burkhard Littwin, and Werner Metzdorf, in their article entitled "X-Bar, a New Propagation Pattern for Magnetic Bubbles", published in the "IEEE Trans. on Magnetics", Vol. MAG-9, No. 3, September 1973, pp. 293-297, these publications being fully incorporated herein by this reference for their teachings of the environmental aspects of memories which may be improved by the practice of the present invention. In these cases, T-shaped, X-shaped and Y-shaped elements serve as individual elements. The German published application No. 1,917,746 discloses Ti-manipulation patterns and patterns comprising rectangular individual elements, the direction of which is inclined toward the path of the cylindrical domains.
Conventionally, in order to provide a low-cost and space-saving memory, it is endeavored to produce a memory having a high bit density, i.e. involving low costs per bit. Storage chips comprising, e.g. 5 .times. 5 mm storage layers, provided with transport structures and conductor loops are in common use. The current storage capacity which can be achieved by means of photolithographic processes, i.e. the storage chip capacity, is 64 k-bits. It is not possible to increase the fineness of the propagation structures employed in the storage loops beyond the storage capacity by employing photolithographic processes.
As is known from the article "Magnetic Bubbles--An Emerging New Memory Technology", by Andrew H. Bobeck, Peter I. Bonyhard and Joseph E. Geusic, published in the "Proc. of the IEEE", VOL. 63, No. 8, August 1975, pp. 1176-1195, also fully incorporated herein by this reference, and from the aforementioned Cohen et al article, it is in fact possible to employ electron beam lithography to produce the conductor loops and transport structures, e.g. manipulation patterns, for the desired storage chip capacities of 256 k-bits and greater, but from the technical viewpoint this process is extremely expensive and complicated, and furthermore does not feature the short cycle times of conventional photolithography. Therefore, for example, by new developments as described in the Cohen et al publication, attempts have been made to achieve high storage densities without imposing strict requirements on the structure production.